Im juz curious n worried abt my period.?

hai.i had arnd 2-3 times with my partner aft my last mens.the thing is i cant remember exactly wen was my last mens.n i tink im late for my current mens.we did use protection though and everytime he pull it outs n shoot on me.so shld i b woried?and wat may b the reasons im late for my next mens?pls help.thank you